When arranging a heat generating electrical component on a circuit board, it may be desireable to dissipate the generated heat using some type of heat sink. One example of heat generating components is light emitting diodes (LEDs).
Light emitting diodes (LEDs) are attractive for a wide range of lighting applications for reasons such as efficiency and long life time compared to conventional lighting such as incandescent and fluorescent bulbs. Nevertheless, in many applications, the heat developed by the LED causes reduced efficiency and influences long-term reliability of LED devices. Consequently, thermal management of LEDs is crucial for proper operation and extended life time.
An LED is typically encapsulated in transparent resin which is poor thermal conductor. Thus, most of the heat produced is conducted through the backside of the LED chip. Therefore, to maintain low junction temperature and keep good performance of the LED, LED devices are typically provided with a heat sink. FIG. 1 illustrates a typical prior art arrangement, where an LED 1 is mounted to a printed circuit board (PCB) 2. The PCB 2 comprises copper sheets 3, 4 laminated onto either side of a dielectric substrate 8. Typically, there are electrical circuit traces etched from the upper copper sheet 3 (i.e. the copper sheet facing the LED) to provide appropriate circuitry. The copper sheets 3, 4 arranged on either side of the PCB 2 also serves as thermally conductive layers 3, 4. These thermally conductive layers 3, 4 are linked by a series of thermal vias 5. The LED 1 is soldered to the PCB 2, wherein PN junction of the LED 1 is electrically connected to the electrical circuit traces of the PCB. The soldering also provides thermal contact between the PN junction and the upper thermally conductive layer 3 of the upper copper sheet 3. The printed circuit board 2 is typically mounted to a heat sink 6 using screws 7. The arrangement may also be provided with a thermal paste to improve thermal contact between the heat sink 6 and the thermally conductive layer 4 facing the heat sink. Through this arrangement, heat generated at the LED junction is conducted through the thermally conductive layers 3, 4 of the printed circuit board 2 and to the heat sink 6 and then to the ambient environment.
However, the multi layer PCB described above may be to expensive to be utilized in low cost applications. Furthermore, as the PCB is attached with screws to the heat sink, differences in coefficient of thermal expansion (CTE) between the PCB and the heat sink may result in stress, causing the printed circuit board to bend and the LED to tilt.